Mari Lou Balmer

Selective Reduction of NOx in Oxygen Rich Environments with Plasma-Assisted Catalysis: The Role of Plasma and Reactive Intermediates

Catalytic activity of selected materials (BaY and NaY zeolites, and g-Alumina) for selective NOx reduction in combination with a non-thermal plasma was investigated. Our studies suggest that aldehydes formed during the plasma treatment of simulated diesel exhaust are the important species for the reduction of NOx to N2. Indeed, all materials that are active in plasma-assisted catalysis were found to be very effective in the thermal reduction of NOx in the presence of aldehydes. For example, the thermal catalytic activity of a BaY zeolite with aldehydes gives 80-90% NOx removal at 250 C with 200ppm NOx at the inlet, 1000ppm of C1 as acetaldehyde, propionaldehyde, and butyraldehyde, and SV=12,000 h?. The hydrocarbon reductants, n-octane and 1-propyl alcohol have also shown high thermal catalytic activity for NOx removal over BaY, NaY and g-alumina. We believe that this activity is due to the fact that in an oxygen rich environment these compounds can be thermally oxidized over the catalysts to form the important aldehyde reaction intermediates.

The structure and properties of two new silicotitanate zeolites

Two new zeolitic crystalline phases with stoichiometry, CSTiSi 2 O 6.5 and CS 2 TiSi 6 O 15 , have been discovered. CSTiSi 2 O 6.5 has a crystal structure isomorphous to the mineral pollucite, CsAlSi 2 O 6 , with Ti +4 replacing Al +3 . This replacement requires a mechanism for charge compensation. A combination of techniques including neutron diffraction, single crystal x-ray diffraction and x-ray absorption spectroscopy have revealed that eight extra oxygens are present per unit cell Cs 2 TiSi 2 O 6.5 as compared to pollucite. As a result of the extra oxygen, the titanium coordination geometry is five-fold. Pentacoordinate titanium and tetrahedral silicon form a network structure with Cs residing in cages formed by the network. The crystal structure of Cs 2 TiSi 6 O 15 is unique, with titanium octahedra and silicon tetrahedra forming an open framework structure with the Cs residing in large cavities. The largest covalently bonded ring opening to the Cs cavities in both compounds are smaller than a Cs ion, revealing that the Cs ion has minimal mobility in the structure. Cesium leach rates for both compounds are lower than or comparable to borosilicate glass.

Effect of Simulated Diesel Exhaust Gas Composition and Temperature on NOx Reduction Behavior of Alumina and Zeolite Catalysts in Combination With Non-Thermal Plasma

NOx reduction under simulated lean burn conditions was studied using a non-thermal plasma in combination with zeolite and alumina catalysts. The influence of temperature and plasma treatment on the catalytic performance was investigated. Zeolite catalyst B showed high activity in the 150-300 degree Celcius temperature region. Alumina Catalyst D was most active at temperatures higher than 250 degrees Celcius. In addition, the alumina catalyst was effective in oxidation of aldehydes formed during plasma treatment of the reaction mixture. When the reaction was carried out over a catalyst bed consisting of separate layers of the zeolite and alumina catalyst, the catalyst temperature range for significant NOx reduction was expanded to 150-500 degrees Celcius.